Conventional automobile braking systems normally operate by applying fluid pressure to a friction means which engages either a wheel disc or wheel drum to effect the braking action. The applied hydraulic pressure is directly under control of the brake pedal although a fluid pressure amplifying system as in the case of power brakes may be provided. As the brake pedal is applied, constant or increasing hydraulic pressure is applied to the friction means to thereby "grip" the wheel disc or drum. Such sudden "gripping" by the friction means can result in a "locking" condition; that is, rotation of the wheel is stopped completely resulting, more often than not, in dangerous skidding. Slower braking action can be applied to permit the wheel to still rotate and yet be slowed by friction of the friction means, but such is not possible in an emergency situation where rapid stopping of the vehicle is necessary.
The foregoing condition is avoided by "pumping" the brakes; that is, periodically releasing the brake pressure to decrease the hydraulic fluid pressure on the friction engaging means so that a series of gripping action results to slow the wheel.
While the foregoing "brake pumping operation" can effectively slow the vehicle in a controlled manner by skilled drivers, a driver under hazardous circumstances may panic and simply jam the brake pedal to the floor and hold it in such condition. A need accordingly exists to provide some mechanism for overcoming such conditions; that is, some type of automatically controlled braking system which will operate without the necessity of a driver "pumping the brakes". Such systems might have particular advantage in racing cars.